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Dimension stone

Dimension stone is natural stone or rock that has been selected and fabricated (i.e., trimmed, cut, drilled, ground, or other) to specific sizes or shapes. Color, texture and pattern, and surface finish of the stone are also normal requirements. Another important selection criteria is durability, the time measure of the ability of dimension stone to endure and to maintain its essential and distinctive characteristics of strength, resistance to decay, and appearance.

Quarries that produce dimension stone or crushed stone (used as construction aggregate) are interconvertible. Since most quarries can produce either one, a crushed stone quarry can be converted to dimension stone production. However, first the stone shattered by heavy and indiscriminate blasting must be removed. Dimension stone is separated by more precise and delicate techniques, such as diamond wire saws, diamond belt saws, burners (jet-piercers), or light and selective blasting with Primacord, a weak explosive.

The commonest finish mentioned below is polished. A polished finish is one having a surface with high luster and strong reflection of incident light (almost mirror-like). The rougher finishes are bush-hammered, honed, sandblasted, and thermal. A bush-hammered finish is one with a rough uniformly patterned surface produced by an impact tool. A honed finish is one with a superfine, smooth, satinlike, nonreflective surface. A sandblasted surface is one with an irregular pitted surface produced by impacting sand particles at high velocity against a stone surface. A thermal (or flamed) finish is one with a rough nonreflective surface with only a few reflections from cleavage faces, produced by applying a high-temperature flame. This finish may change the natural color of the stone.

The most easily-accessible general references are the latest (2006) Minerals Yearbook Chapter (production and foreign trade, with statistics), and the latest (Issue 30) Dimension Stone Advocate News (new "building green" developments and demand statistics); see below.

Major applications

While some common colors used in some of the major applications are listed below, stone in every color of the rainbow and every shade imaginable are also used, in thousands of patterns. These patterns are created by geological phenomena such as mineral grains, inclusions, veins, cavity fillings, blebs, and streaks, to name a few. In addition, rocks and stones that are not considered dimension stone are sometimes selected for these applications. For example, tiles made of jade, agate, and jasper are available. A rose quartz tombstone stands in a Harpers Ferry WV cemetery.

Countertops and bathroom vanities both involve a finished slab of stone, usually polished but sometimes with another finish (i.e. honed, sandblasted). Industry standard thicknesses are 3/4" (2 cm) and 1.25" (3cm). Often the 2 cm slabs will be lamintated at the edge to create the appearance of a thicker edge profile. The slabs are cut to fit the top of the kitchen or bathroom cabinet, by measuring, templating or digital templating. Countertop slabs are commonly sawn from rough blocks of stone by reciprocating gangsaws using steel shot as abrasive. More modern technology utilizes diamond wire saws which use less water and energy. Multi-wire saws with as many as 60 wires can slab a block in less than two hours. The slabs are finished (i.e., polished, honed), then sealed with resin to fill micro-fissures and surface imperfections typically due to the loss of poorly bonded elements (e.g.biotite). The fabricators shop cuts these slabs down to final size and finishes the edges with equipment such as hand-held routers, grinders, CNC equipment, or polishers. The stone for countertops or vanities is usually granite, but often is marble (especially for vanity tops), and sometimes limestone or slate. The great majority of the stone for this application is imported, mostly from Brazil, Italy, and China.

Tile is a thin modular stone unit, commonly 12 in. square (30.5 cm) and 3/8 in. (10 mm) thick. Other popular sizes are 15 in. square (38 cm), 18 in. square (46 cm), and 24 in. square (61 cm); these will usually be thicker than the 12 in. square. The great majority of tile has a polished finish, but other finishes such as honed are becoming more common. Almost all stone tile is mass-produced by automated tile lines to identical size, finish, and close tolerances. Exceptions would include slate flooring tile and special orders: tile with odd sizes or shapes, unusual finishes, or inlay work. In summary, the automated tile line is a complicated complex of cutting and calibrating machines, honing-polishing machines, edging machines that put on flat or rounded edges, and interconnecting conveyors to move the stone from the slab input to the final tile product. The stone for tiles is most commonly marble, but often is granite, and sometimes limestone, slate, or quartz-based stone. Commoner colors are white and light earth colors. Almost all of the stone for this application is imported, from countries such as Italy and China.

Monuments include stone used as tombstones, grave markers or as mausoleums. After being gangsawed into big thick (up to . long and over 6 in. thick) slabs, smaller saws or guillotines (they break the granite and make the rough edges commonly seen on monuments) shape the monuments. The fronts and backs are very commonly polished. The individual monuments are then carved, shaped, and further defined by hand tools and sandblasting equipment. The stone for monuments is most commonly granite, sometimes marble (i.e. in military cemeteries), and rarely others. The commoner monument colors for granite are gray, then black, then mahoghany; for marble it is white. The vast majority of the stone used in North America in this application is imported from such countries as India and China. This has depressed traditional North American monument centres such as Georgia and Quebec.

There are a number of smaller applications for buildings and traffic-related uses. Building components include stone used as veneer (exterior), ashlar, or other shapes. Veneer is a nonload-bearing facing of stone attached to a backing, of an ornamental nature though it protects and insulates. Ashlar is a square block of stone, often brick-sized, for facing of walls (primarily exterior). The other shapes are rectangular blocks used for stair treads, sills, and coping (coping is sometimes nonrectangular). The shapes subject to foot traffic will usually have an abrasive finish such as honed or sandblasted. The stone is mostly limestone, but often is quartz-based stone (sandstone), or even marble or granite. Roofing slate is a thin-split shingle-sized piece of slate, and when in place forms the most permanent kind of roof; slate is also used as countertops and flooring tile. Traffic-related stone is that which is used for curbing (vehicular) and flagstone (pedestrian). Curbing is thin stone slabs used along streets or highways to maintain the integrity of sidewalks and borders. Flagstone is a thin naturally irregular-edged slab of stone, sometimes sawed into a rectangular shape, used as paving (almost always pedestrian). For curbing, the stone is almost always granite, and for flagstone the stone is almost always quartz-based stone (sandstone or quartzite).

There are several other applications resembling flagstone in using rough dimension (or crushed) stone, usually as quarried, sometimes made smaller (i.e. by a jackhammer), often simply put in place: dry stone and riprap.

The stone used in these applications usually has to have certain properties, or meet a standard specification. The American Society for Testing and Materials (ASTM) has such specifications for granite (C615), marble (C503), limestone (C568), quartz-based dimension stone (C616), slate (C629), travertine (C1527), and serpentine (C1526).

Production

The majors producers of dimension stone include Brazil, China, India, Italy, and Spain, and each have annual production levels of nine to over twenty-two million tons. Portugal produces 3 million tons of dimension stone each year.

According to the USGS, 2006 U.S. dimension stone production was 1.33 million tons valued at $265 million, compared to 1.36 million tons (revised) valued at $269 million in 2005. Of these, granite production was 428,000 tons valued at $105 million in 2006 and 416,000 tons valued at $106 million in 2005, and limestone was 559,000 tons valued at $96.1 million in 2006 and 581,000 tons valued at $95.8 million (revised) in 2005. The United States is at best a mid-level dimension stone producer on the world scene; Portugal produces twice as much dimension stone annually.

World comparison for dimension stone demand: The DSAN World Demand for (finished) Granite Index showed a growth of 15% annually for the 2000-2006 period, compared to 14% annually for the 2000-2005 period. The DSAN World Demand for (finished) Marble Index showed a growth of 12% annually for the 2000-2006 period, compared to 10.5% annually for the 2000-2005 period. Other DSAN indexes for 2007 (preliminary) indicate that the 2000-2007 growth probably will be down from the 2000-2006 growth.

The DSAN U.S. Ceramic Tile Demand Index shows a growth of 5.0% annually for the 2000-2006 period, compared to 5.5% annually for the 2000-2005 period. The "traditional" major ceramic tile suppliers, Italy and Spain, have been losing markets to new entrants Brazil and China. The same thing has been happening with dimension stone with increasing supplies from Brazil, China and India.

The Chinese Government has made a policy shift of long-term worldwide significance for dimension stone production and demand by eliminating the 15% export tax rebate on all dimension stones. It is replacing it with a 10% to 15% export tariff on minerals and stones. In addition, the Chinese Government sometimes strongly discourages its domestic firms from buying rough dimension stone overseas.

"Building green" with dimension stone

Green building or environmentally friendly construction with natural materials, is an idea that has been around for several decades. Energy price increases and the need for energy conservation when heating or cooling buildings have recently brought it to the fore. This resulted in the formation in 1993 of the U.S. Green Building Council (USGBC), which has developed a building rating system LEED. Educational institutions (colleges, universities, grade, and high schools) are often requiring new buildings to be green, and a few jurisdictions (i.e., some cities) have some rules pushing green building. When "building green", dimension stone has a big advantage over concrete, aluminum, and steel, whose productions are all highly energy intensive. As an entirely natural product, dimension stone also has an advantage over quartz surface artificial stone (resin-agglomerated stone) made from mixed quartz sand or ground stone and a resin (i.e., acrylic). One LEED requirement provides that the dimension stone used in a green building be quarried within a radius of the building being constructed. This gives a clear advantage to domestic dimension stone, plus some quarried near the U.S. borders with Canada and Mexico. A current problem is how to consider stone quarried domestically, sent to China or Italy for finishing, and shipped back to be used in a project. Dimension stone also has the advantage from a green perspective of being recyclable and can often be recycled and not sent to a landfill. There are also "green" ways of cleaning stone being developed; for example, removing the black gypsum crusts that form on marble and limestone by applying sulfate-reducing bacteria to the crust to gasify most of it, breaking up the crust. See DSAN for updates on "building green" and dimension stone recycling.

Stone recycling and reuse

Recycling dimension stone can occur when structures are demolished, along with recycling timber and recycling construction aggregate in the form of concrete. The material most likely to be recycled is concrete, and this represents the largest volume of recycled construction material. Not too many structures incorporate dimension stone, and even less of them have dimension stone worth saving. Stone recycling is usually done by specialists that monitor local demolition activity, looking for stone-containing houses, buildings, bridge abutments, and other dimension stone structures scheduled for demolition. Particularly treasured are old hand-carved stone pieces with the chisel marks still on them, local stones no longer quarried or that are quarried in a different shade of color or appearance. There is no national or regional trade in reclaimed stone, so a large storage yard is required, since the recovered stone may not be quickly sold and reused. The recycled dimension stone is used in old stone buildings being renovated (to replace deteriorated stone pieces), in fireplace mantels, benches, veneer, or for landscaping (like for retaining walls).

Related to stone recycling and stone reuse is the deconstruction and reconstruction of a stone building. The building is taken apart stone block by stone block and the location and orientation of each block is carefully noted. Any roofing slate and interior stone in place is catalogued and moved in the same fashion. After transporting the blocks, slate, and other stone used to the new location, they are put back in place where and how they were originally, thus reassembling the building. This has been a very uncommon occurrence, but will probably become more common in the future.

Dimension stone is also reused. Buildings immediately spring to mind, but such things as the ornate stone walls, arches, stairways and balustrades alongside a boulevard can also be renovated and reused. Sometimes the old interior of the building is kept as is, after repair. Sometimes the old building is gutted, leaving only a shell or facade and the space inside reconfigured and modernized. The stone work will usually need attention too.

The old stone work may only need cleaning or sandblasting, but it may need more. The most likely needs are mortar restoration (repointing) or replacing pieces of stone that are deteriorated (damaged) beyond the point of any repair. The repointing is the removal of existing damaged mortar from the outer portion of the joint between stone units and its replacement by new mortar matching the appearance of the old. Deteriorated pieces of stone work are replaced with pieces of stone that match the original as much as possible. Exterior dimension stone will often change color after exposure to weather over time. For example, Indiana Limestone will weather from a tan to an attractive light yellow. Interior dimension stone can sometimes change its shade a little over time too. For both, it may not be possible to find an exact match, even from the original quarry. Stone will often change its appearance from location to location in the same quarry. If the dimension stone renovationist is truly fortunate, the original builder put aside some spare pieces of the stone for future need.

Stone selection and cleaning

The selector of dimension stone begins by considering stone color and appearance, and how the stone will match its surroundings. The selector has literally literally thousands of options to choose from, and should examine many options. In addition to many hundreds of different stones with different colors and patterns, each stone can change radically in color and appearance when a different finish is put on it. A polished finish accentuates the color and makes any pattern more vivid, and the rougher finishes (i.e. honed, thermal) lighten the color and make the patterns more subdued. With thousands of possibilities, the selector must start by looking at many stones in many different finishes, or photos of them. Such photos can be found on some dimension stone websites, and on DSAN's Architects Stone Selection Helper.

In addition to selecting a stone color and pattern, the suitability of its properties for the intended use must be considered. Stone being chosen for countertops or vanities should be nonabsorptive, resist stains, and be heat and impact resistant. Stone being used in tiles should be sealed in order to resist staining by spilled liquids. Stone being used for flooring, paving, or surfaces subject to foot or vehicular traffic ought to have a semiabrasive finish for slip resistance, such as bush-hammered or thermal. A glossy polished finish will be slick. Most flagstone surfaces are rough enough to be naturally slip-resistant. The ASTM document C1528 Standard Guide for Stone Selection is very helpful, and covers topics not mentioned here.
Dimension stone requires some specialized methods for cleaning and maintenance. Abrasive cleaners should not be used on a polished stone finish because it will wear the polish off. Acidic cleaners can not be used on marble or limestone because it will remove (i.e. dissolve) the finish. Textured finishes (thermal, bush-hammered) can be treated with some mildly abrasive cleaners but not bleach or an acidic cleaner (if marble or limestone). Stains are another consideration; stains can be organic (food, grease, or oil) or metallic (iron, copper). Stains require some special removal techniques, such as the poultice method. A new method of cleaning stone on ancient buildings (midaeval and renaissance) has been developed in Europe: sulfur-reducing bacteria are used on the black gypsum-containing crusts that form on such buildings to convert the sulfur to a gas that dissipates, thus destroying the crust while leaving the patina produced by aging on the underlying stone. This method is still in development and not commercially available yet. The ASTM document C1515 Standard Guide for Cleaning of Exterior Dimension Stone is also very helpful, and covers problems and remedies not mentioned here.